Fix DSV export for NUL bytes

[DhruvShah-Dev]

What type of PR is this?

Bug fix

Description

CSV and TSV export can fail when query results contain embedded NUL bytes because Python's CSV writer raises while trying to escape those values. This change removes NUL bytes from string fields before DSV serialization and avoids mutating the stored query result row during export.

Fixes #7758

Validation

• git diff --check
• python -m pytest tests\serializers\test_query_results.py (blocked locally: missing Redash runtime dependency redis)

[greptile-apps]

Greptile Summary

The PR prevents embedded NUL bytes from breaking CSV and TSV exports while preserving stored query-result rows.

• Adds DSV-specific string sanitization that removes NUL bytes.
• Copies each row before applying type conversions, avoiding mutation during export.
• Adds regression coverage for exporting a string containing an embedded NUL byte.

Confidence Score: 5/5

The PR appears safe to merge.

No blocking failure remains.

Important Files Changed

Filename	Overview
redash/serializers/query_result.py	Sanitizes string values immediately before DSV writing and performs conversions on a shallow row copy.
tests/serializers/test_query_results.py	Adds focused regression coverage confirming embedded NUL bytes are removed from exported string fields.

_{Reviews (2): Last reviewed commit: "Apply backend formatter" | Re-trigger Greptile}

[cubic-dev-ai]

No issues found across 2 files

_{Re-trigger cubic}

[DhruvShah-Dev]

Updated this PR with a formatting-only commit to satisfy backend-lint.

Validated locally:

• python -m black --check redash\serializers\query_result.py tests\serializers\test_query_results.py
• python -m ruff check redash\serializers\query_result.py tests\serializers\test_query_results.py

The targeted pytest command still cannot collect locally because this checkout is missing the Redash runtime dependency redis.

[yoshiokatsuneo]

The python CSV exportor issue looks already being solved on the Python3.13.
I can suggest to test the issue on the latest Redash and the latest usable Python(3.13).

python/cpython#97503

[DhruvShah-Dev]

Closing this after testing the same csv.DictWriter path on Python 3.13.3, where a value containing \x00 writes successfully without raising.

Given that the original failure is no longer reproducible on the current supported Python version, withdrawing this sanitization change.